It is known to chemically sensitize photographic silver halide emulsions with a variety of chemical compounds, e.g., noble metal compounds, compounds providing labile sulfur or selenium, etc. Chemical sensitization is considered to result from the formation of silver sulfide specks on the silver halide crystals resulting from the presence of labile sulfur or from the formation of silver specks on the silver halide crystals resulting from the presence of a reduction sensitizer. The sensitizing activity of sulfur and selenium on silver halide emulsions has been well documented, and compounds which have been used in conjunction with these elements are the organic phosphites and organic phosphine compounds. However, there is need for a stronger sensitizer.